docs: def leader_set(settings=None, **kwargs):
      """Juju leader set value(s)"""
      # Don't log secrets.
      # log("Juju leader-set '%s'" % (settings), level=DEBUG)
      cmd = ['leader-set']
      settings = settings or {}
      settings.update(kwargs)
      for k, v in settings.items():
          if v is None:
              cmd.append('{}='.format(k))
          else:
              cmd.append('{}={}'.format(k, v))
      subprocess.check_call(cmd)